This investigation is designed to follow prospectively a cohort of approximately 120,000 women, ages 30-54, in whom exposure to oral contraceptives, estrogens, cigarette smoking, and hair dyes has been documented. Morbidity and mortality for a variety of cancers including breast, endometrial, ovary, and others, as well as cardiovascular events, benign breast disease, and other benign obstetric and gynecologic events such as infertility and outcome of pregnancies will be followed. The approach is by mail questionnaire with further documentation of events by review of hospital records and pathologic specimen. The cohort was defined from the register of Registered Nurses collected by the American Nurses' Association in 1972 and recorded at that time as being married women. Those women who on January 1, 1976 were between the ages of 30-54 and who responded to an inquiry in 1976 which collected - besides data mentioned above - information on menstrual history, height, weight, current contraceptive status and family history of myocardial infarction and breast cancer in female relatives constitute the cohort. In addition, an estimate of social class status at age 16, based upon parental occupations, was obtained. Personal past medical events related to cardiovascular, thromboembolic, benign and malignant breast disease, and other cancers were collected also. These variables will be used in multivariate models to define levels of risk of the above-mentioned outcome events.